This invention relates generally to polyfluorinated diisocyanates and a method of synthesizing them. More particularly, the invention relates to such diisocyanates defined by the formula OCN--CH.sub.2 CH.sub.2 --(CF.sub.2).sub.n --CH.sub.2 CH.sub.2 --NCO, wherein n is a whole number of from 2 to 16, inclusive.
Diisocyanates are known to be useful for the preparation of polyurethanes and polyureas, and fluorocarbon segments are known to generally impart favorable dielectric, water-repellency and anti-fouling properties to polymer systems. The synthesis of the perfluoroalkylene diisocyanates OCN--(CF.sub.2).sub.n --NCO by the Curtius rearrangement of the corresponding acyl azides has been reported--Knunyants, I. L.; Krasuskaya, M. P.; Del'tsova, D. P. Izv. Akad, Nauk SSSR, Ser. Khim., Engl. Ed., 1066 (1966). Reactions of these isocyanates with alcohols give urethanes including and characterized by the structure --CF.sub.2 --NH--CO.sub.2 R. Compounds with NH groups adjacent to CF groups generally have a tendency toward instability because of the elimination of HF. The synthesis of tetrahydroperfluoroalkylene diisocyanates, OCN--CH.sub.2 --(CF.sub.2).sub.n --CH.sub.2 --NCO, has also been reported. See Takakura, T.; Yamabe, M.; and Kato, M., Nippon Kagaku Kaishi, 2208 (1985), where the method of synthesis involved the Curtius rearrangement of the corresponding acid azides.
The most commonly used method for the synthesis of commercially important isocyanates is the reaction of phosgene with amines or amine salts. See Babad, H.; Zeiler, A. G., Chem. Rev., 73, 75 (1973) and Farlow, M. S., Org. Syn., Coll. Vol. IV, 521. The amine reacts with phosgene to yield the corresponding carbamoyl chloride which then loses hydrogen chloride to form the isocyanate. EQU RNH.sub.2 +COCl.sub.2 .fwdarw.RNHCOCl.fwdarw.RNCO+HCl